End of Train Device (ETD)
The End of Train Device (ETD), sometimes referred to as an EOT, FRED (Flashing Rear-End Device) or SBU (Sense and Braking Unit) is an electronic device mounted on the end of freight trains in lieu of a caboose. They are divided into two categories: "dumb" units, which only provide a visible indication of the rear of the train with a flashing red taillight; and "smart" units, which sends back data to the crew in the locomotive via radio-based telemetry. They originated in North America, and are also used elsewhere in the world.
Design and use
The "smart" ETD devices monitor functions such as brake line pressure and accidental separation of the train using a motion sensor, functions that were previously monitored by a crew in the caboose. The ETD transmits the data via a telemetry link to the Head-of-Train Device (HTD) in the locomotive, known colloquially among railroaders as a "Wilma." This is a play on the first name of the wife of cartoon character Fred Flintstone. In Canada, this device is known as an SBU (Sense and Braking Unit).
A typical HTD contains several lights indicating telemetry status and rear end movement, along with a digital readout of the brake line pressure from the ETD. It also contains a toggle switch used to initiate an emergency brake application from the rear end. In modern locomotives, the HTD is built into the locomotive's computer system, and the data is displayed on the engineer's computer screen.
Railroads have strict government-approved air brake testing procedures for various circumstances when assembling trains or switching out cars en route. After a cut is made between cars in a train and the train is rejoined, in addition to other tests, the crew must verify that the brakes apply and release on the rear car (to ensure that all of the brake hoses are connected and the angle cocks, or valves, are opened). In most cases, the engineer is able to use data from the ETD to verify that the air pressure reduces and increases at the rear of the train accordingly, indicating that proper brake pipe continuity. This device is said to constitute a fail-safe condition.
The ETD reduced labor costs, as well as the costs of the purchase and upkeep of cabooses. The Brotherhood of Conductors, and Brotherhood of Railroad Brakemen were also greatly affected by ETD, as this electronic unit replaced two crewmen per train. The widespread use of ETD's has made the caboose nearly obsolete. Some roads still use cabooses where the train must be backed up, on short local runs, as rolling offices, or railroad police stations and as transportation for right-of-way maintenance crews.
The first ETD use is attributed to Florida East Coast Railway in 1969, soon after which other Class I railroads began using ETD's as well. By the mid-1980s they were common equipment. Early models were little more than a brake line connection / termination, a battery and flashing tail light. As their use became more widespread through the 1980s, ETD's were equipped with radio telemetry transmitters to send brake pressure data to a receiver in the locomotive. To reduce the cost of battery replacements, ambient light sensors were added so the flashing light on the ETD would illuminate only during dusk and after dark. Later models have a small turbine-powered electrical generator using air pressure from the brake line to power the ETD's radio and sensors.
The one-way communication of brake data from the ETD to the locomotive evolved into two-way communication that enables the engineer to apply the brakes from both ends of the train simultaneously in an emergency. This is useful in the event that a blockage (or an unopened valve) in the train's brake line is preventing dumping the air pressure and causing all of the brakes in the train going into an emergency application. Such a situation could be dangerous, as stopping distance increases with fewer functioning brakes. Dumping the brake line pressure from both the front and rear of the train simultaneously ensures that the entire train applies all of its brakes in emergency. Other electronics within the ETD were also enhanced, and many now include GPS receivers as well as the two-way radio communications.
Railfans and railway photographers sometimes monitor the ETD frequencies as an early warning system to detect approaching trains. ETD's in North America operate on the 452.9375/457.9375 MHz frequency pair, with the train on the higher frequency and locomotive on the lower; Norfolk Southern Railway originally used AAR channel 67 (161.115 MHz). but has gradually converted to the standard UHF frequencies. Railfans often program these frequencies into their radio scanners, which can provide a handy indicator of train activity (usually 2–5 miles, transmitting at 2 watts).
In Australia a number of safeworking systems require end-of-train devices on trains. They vary from simple flashing lights with no air brake connection, to complete End of Train Air System (ETAS) or Sense and Brake Unit (SBU) devices. During the 1980s these devices rapidly replaced Guard's vans at the rear of most freight services and came to be nicknamed 'Battery Operated Guard' or 'BOG'.
- Lustig, David (August 2006). "End-of-train devices keep on evolving in back". Trains 66 (8): p 18. ISSN 0041-0934.
- Robert S. McGonigal (May 1, 2006). "End-of-train devices". TRAINS Magazine. www.trains.com. Retrieved 2010-05-27.
- "Wongm's Rail Gallery - ETM devices". railgallery.wongm.com. Retrieved 2010-05-27.
- "VICSIG - Infrastructure - Safeworking in Victoria". www.vicsig.net. Retrieved 2010-05-27.